Primers, which are compositions that promote the adhesion of overcoatings onto substrates, are known in the art. They are particularly useful in articles requiring that organic materials be bonded onto inorganic substrates. The strength of the interfacial bond formed in such constructions often determines the ultimate strength and utility of the articles.
Previous attempts have been made to overcoat aluminum and other metals with various substances, but the resulting adhesion of the overcoating is frequently less than is necessary for the desired use. U.S. Pat. No. 3,321,350 teaches that adhesion of a cured polysiloxane onto a solid material, e.g., aluminum, is improved if a primer containing an organosilane and a hydrolyzable titanium compound, some of which primers are within the scope of the primer compositions of the present invention, is first applied. It is taught in U.S. Pat. No. 3,794,556, that a primer composition comprising a mixture of a tetraalkoxysilane, or a partial hydrolyzate thereof, and a tetraalkyl titanate can be used to improve the adhesion of silicone elastomers to titanium metal and to polymerized substrates, such as cured epoxy surfaces and polyurethanes. However, it is not taught in the prior art how to adhere a coating that is polymerized in situ on aluminum or other inorganic substrates with a superior level of adhesion needed in certain applications.
Titanium compounds have been used in preparing durable coatings. U.S. Pat. No. 2,721,855 teaches that polymeric organosilicone compositions containing titanic acid esters adhere onto various substrates, such as electrical insulators. U.S. Pat. No. 3,779,991 discloses the incorporation of tetraalkyl titanates into polymeric materials having silicon and hydantoin moieties in the polymeric backbone, and the subsequent use of such materials as coatings for wire. A composition and method for enhancing bonding and protection of aluminum surfaces is disclosed in U.S. Pat. No. 3,687,882, wherein the adherent coating is derived from a cohydrolyzed composition of a diaminosubstituted silane and a titanate. Galvanic protection to metal surfaces coated with compositions containing hydrolyzed and condensed organosilanes with hydrolyzable titanate esters and zinc particulates is taught in U.S. Pat. No. 3,817,905.
Compositions comprising silanes and metal esters, some within the scope of the primer compositions of the present invention, have been disclosed in U.S. Pat. Nos. 4,042,749, 4,073,967, and 4,084,021 as useful abrasion or corrosion resistant coatings for soft surfaces, including aluminum. These are relatively thick coatings and they are not taught as useful primer compositions.
The prior art, however, does not teach the promotion of adhesion of polymerizable monomeric organic materials, such as epoxy or acrylic monomers, onto primed inorganic surfaces such as aluminum metal, preferably where the primer composition contains acidic material in addition to silanes and metal esters, nor does it teach the curing of monomeric organic coatings by in situ polymerization of the monomers coated onto the primed surfaces.